A Biogeographical Debate at the Origins of Limnology in Switzerland and Italy: The Issue over Pelagic Fauna Between Pietro Pavesi and François-Alphonse Forel.

This article explores the early biogeographical debates that shaped the beginning of limnology, focusing on the differences of opinion concerning the origins of pelagic fauna between two pioneering scientists: Pietro Pavesi and François-Alphonse Forel. The study examines how Pavesi's hypothesis of a marine origin for pelagic fauna contrasts with Forel's theory of passive distribution, situating their arguments within a broader Darwinian framework. The first part of the paper provides a historical overview of Italian limnology, highlighting Pavesi's contributions and interpreting Forel's writings to underscore the significance of discovering pelagic fauna in conceptualizing lakes as microcosms. The second part compares Pavesi's and Forel's hypotheses, emphasizing their impact on the scientific understanding of freshwater ecosystems. The importance of this discovery, in both historical and scientific contexts, lies in recognizing the presence of plankton in lakes as a crucial element for the mature formulation of ecological concepts, such as the ecosystem.